This abstract reports the major findings from the second year of the project: Critical conditions for formation of gas emboli have never been precisely defined but should be more easily determined with fluid rather than air breathers because gas and hydrostatic pressure can be varied semi-independently in the external environment. To define the relevant parameters, the response of both juvenile and adult salmonids to supersaturation imposed (1) internally by decompression from saturation and (2) externally by sudden exposure to supersaturated water was studied in a specially designed two-compartment chamber using a variety of oxygen and inert gas mixes (20% oxygen and 80% inert gas). Hematological investigations on fish similarly exposed to lethal and non-lethal decompressions showed prolonged prothrombin and partial thromboplastin times combined with decreased fibrinogen levels. These changes are indicative of consumptive coagulation following decompression. The time of bubble appearance in the dorsal aorta, and the subsequent stress behavior was studied using doppler-tipped catheter. In a one-kilogram fish, bubble signals occurred within 10 minutes of exposure to highly supersaturated water at one atmosphere. Signs of distress were observed 5 minutes later and death occurred at 20 minutes. Postmortems revealed bubbles in direct relation to the degree of tissue perfusion, the most frequent occurrence being in the vascular system and the least frequent in fat and muscle. The results indicate that in this system the well-perfused tissues constitute a critical compartment and for any given decompression, the pressure difference, the pressure ratio and total gas concentration are all factors which should be considered for developing more reliable ascent criteria.